1. Field of the Invention
This invention relates to process control inside a manufacturing facility. Particularly it provides an alternative to statistical process control (“SPC”) methods used in a multi-part number manufacturing facility. More particularly the invention addresses the issue of undetected part number sub-populations being manufactured differently than a larger technology population. Its purpose is to protect the manufacturer's WIP and to ensure product conforms to customer specifications.
2. Background of the Invention
In a multi-part number manufacturing environment, the fabricator offers a set of generic “capabilities” or “technologies” to their customers. Each technology has a set of specifications that the customer's product will achieve. Typically, the newest or latest generation technology has tighter specs or more features resulting in a more advanced product and also a higher price to manufacture. The customer then requests their design be fabricated in a particular technology—one that meets their own criteria within a cost requirement. In this environment, the fabricator will then have individual part numbers for each customer's design, all within some defined technology.
This is the current situation for many semiconductor manufacturers. With the increase in fabless design shops, many more manufacturers are turning into a multi-part number fab.
In a multi-part number fab, the current standard is for SPC control to be done on a technology basis. Since all the individual part numbers within a technology are manufactured with the same processes, they define a single population. Therefore, each control chart contains all the collective part numbers within a single technology. SPC run rules are evaluated against that technology to determine if that technology is out-of-control (OOC). If an OOC event is detected, then that technology is inhibited and cannot continue being manufactured until the inhibit is resolved.
However, this model of industry-standard SPC control has three major impediments for the multi-part number fab: 1) the customer's product is at risk of being OOC and undetected by SPC within the larger technology population, 2) true SPC limits are defined by the capability of the manufacturing process and not the customer requirements and 3) the manufacturer can inhibit the entire technology for an OOC event that may be limited to one part number.